This article gives a good account of the pros and cons. Combined with no two-a-days, it will eat into summer school. I would not push the conference championships back a week in December because of conflict with finals. If anything, move them up a week as I will describe in a moment. I know other divisions do play during those weeks. That's because they don't have a choice. FBS is different. Not only are you talking the team, it's the band, cheer leaders, managers, trainers, etc. For a typical FBS team, you're talking about messing with the education of 700-800 students. Here are two ideas:
1. Allow the Group of Five schools to open the weekend before Labor Day. Watch how the attention will get sucked to Alabama-FSU, TTUN-Florida, etc. No one pays any attention to the Group of Five (last year's Houston-Oklahoma was an anomoly.) This would give them some limelight. Play doubleheaders to pack NFL stadiums & create some buzz. Would you go to Paul Brown Stadium to see Ohio U.-Ball State and UC-Navy? Or Cleveland to see Kent-Akron and Ohio U.-Ball State if it's the only game in town and you're starved for college football?
2. Power Five schools contract the season by a week. Others stay the course (see above.) Move up the conference championships games to Thanksgiving weekend. Expand the playoffs to eight teams with the top four hosting on campus. Losers still get a good bowl experience while winners proceed as now.
3. Go back to limited two-a-day sessions. I doubt if any team has full contact for both practices. I think lengthening fall practice will cause more harm, both in terms of cost and interference with summer school.